MITF Is an Essential and Functionally Multifaceted Transcription Factor in Cutaneous Melanoma

Melanoma incidence is steadily on the rise but widespread prevention awareness and novel treatment approaches have substantially ameliorated the prognosis of the disease. Microphthalmia-associated transcription factor (MITF) is an essential transcription factor that plays a central role in the transcriptional circuitry of both normal melanocytes and malignant melanoma. Since over 30 years have elapsed since its discovery in mice, a large number of its target genes have been identified in pigment cells. Many upstream regulators of MITF have also been identified. Despite these substantial discoveries, MITF function, especially in melanomas, still remains elusive in several aspects. MITF is absolutely required for melanin formation because it transcribes virtually all genes required for the synthesis, storage, and transport of the pigment. Importantly, MITF is necessary for prevention of apoptosis in melanomas, at least at the early stages. However, in some metastases, MITF may be absent in most cells and its antiapoptotic function is evidently replaced by other proteins that not yet been fully identified. Furthermore, MITF is a specific nevus and melanoma marker, which is routinely used in immunohistochemistry, along with other markers, to distinguish pigmented and other skin lesions. In melanomas, high-MITF melanoma cell subpopulations are considered differentiated, i.e., pigmented and rapidly proliferating. In contrast, low-MITF cells proliferate slowly but are invasive with cancer stem cell-like properties. Although MITF activates mostly antiapoptotic and pro-proliferative genes, it also activates typical cell cycle inhibitors such as the p16 and p21 proteins. Here we discuss the issues of MITF multifunctionality in melanoma and associated research prospects.